CD-ROM Appendix A, which is a part of the present disclosure, is a CD-ROM appendix consisting of 22 text files. CD-ROM Appendix A includes a software program executable on a controller as described below. The total number of compact disks including duplicates is two. Appendix B, which is part of the present specification, contains a list of the files contained on the compact disk. The attached CD-ROM Appendix A is formatted for an IBM-PC operating a Windows operating system.
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
These and other embodiments are further discussed below.
1. Field of the Invention
The present invention relates to an optical disk system and, in particular, to a servo system for controlling and monitoring the operation of an optical disk spin motor control system.
2. Related Art
The need for compact data storage is explosively increasing. The explosive increase in demand is fueled by the growth of multimedia systems utilizing text, video, and audio information. Furthermore, there is a large demand for highly portable, rugged, and robust systems for use as multimedia entertainment, storage systems for PDAs, cell phones, electronic books, and other systems. One of the more promising technologies for rugged, removable, and portable data storage is WORM (write once read many) optical disk drives.
One of the important factors affecting design of an optical system (such as that used in a WORM drive) is the optical components used in the system and the control of actuators used to control the optical system on the disk. The optical system typically includes a laser or other optical source, focusing lenses, reflectors, optical detectors, and other components. Although a wide variety of systems have been used or proposed, typical previous systems have used optical components that were sufficiently large and/or massive that functions such as focus and/or tracking were performed by moving components of the optical system. For example, some systems move the objective lens (e.g. for focus) relative to the laser or other light source. It was generally believed that the relatively large size of the optical components was related to the spot size, which in turn was substantially dictated by designs in which the data layer of a disk was significantly spaced from the physical surface of the disk. A typical optical path, then, passed through a disk substrate, or some other portion of the disk, typically passing through a substantial distance of the disk thickness, such as about 0.6 mm or more, before reaching a data layer.
Regardless of the cause being providing for relative movement between optical components, such an approach, while perhaps useful for accommodating relatively large or massive components, presents certain disadvantages for more compact usage. These disadvantages include a requirement for large form factors, the cost associated with establishing and maintaining optical alignment between components which must be made moveable with respect to one another, and the power required to perform operations on more massive drive components. Such alignment often involves manual and/or individual alignment or adjustment procedures which can undesirably increase manufacturing or fabrication costs for a reader/writer, as well as contributing to costs of design, maintenance, repair and the like.
Many early optical disks and other optical storage systems provided relatively large format read/write devices including, for example, devices for use in connection with 12 inch (or larger) diameter disks. As optical storage technologies have developed, however, there has been increasing attention toward providing feasible and practical systems which are of relatively smaller size. Generally, a practical read/write device must accommodate numerous items within its form factor, including the media, media cartridge (if any), media spin motor, power supply and/or conditioning, signal processing, focus, tracking or other servo electronics, and components associated or affecting the laser or light beam optics. Accordingly, in order to facilitate a relatively small form-factor, an optical head occupying small volume is desirable. In particular, it is desirable that the optical head have a small dimension in the direction perpendicular to the surface of the spinning media. Additionally, a smaller, more compact, optical head provides numerous specific problems for electronics designed to control the position and focus of the optical head.
Additionally, although larger home systems have little concern regarding power usage, portable personal systems should be low power devices. Therefore, it is important to have a system that conserves power (e.g., by optically overfilling lenses) in both the optical system and the electronic controlling system.
In accordance with the present invention, a system and method includes a control system design for controlling operation of a motor system that addresses the design challenges for the small form factor optical disk system. The optical disk system includes a spin motor on which an optical medium is positioned, an optical pick-up unit positioned relative to the optical medium, an actuator arm that controls the position of the optical pick-up unit, and a control system for controlling the spin motor, the actuator arm, and the laser.
Embodiments of the control system and device in accordance with the present invention use several unique methods including sharing a general purpose processor between the servo system and other drive systems in the device, using a dedicated high speed processor for time critical servo functions, communicating between the dedicated servo processor and the shared general purpose processor, distributing the servo processing between the general purpose processor and the dedicated servo processor, and distributing the servo processing within the general purpose processor between a main loop process and a background periodic interrupt process.
In one aspect of the present invention, a method is provided for controlling spin speed. The method includes detecting a first BEMF crossing and setting a first time stamp, detecting a second BEMF crossing and setting a second time stamp; calculating a measured spin period as the difference between the first time stamp and the second time stamp; comparing the measured spin period to a reference spin period to determine a period error; operating on the period error with a proportional gain and an integrator gain to provide a command output; and driving a winding in the spin motor with a current to cause the spin motor to change velocity in response to the command output.
In another aspect of the present invention, a system is provided for controlling spin speed. The system includes a first module operable to detect a first BEMF crossing and setting a first time stamp and to detect a second BEMF crossing and setting a second time stamp. A second module is also included which is operable to calculate a measured spin period as the difference between the first time stamp and the second time stamp, and is also operable to compare the measured spin period to a reference spin period so as to determine a period error. A third module is operable to operate on the period error with a proportional gain and an integrator gain to provide a command output. A fourth module is included which is operable to drive a winding in the spin motor with a current to cause the spin motor to change velocity in response to the command output.
For purposes of summarizing the invention, certain aspects, advantages, and novel features of the invention have been described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any one particular embodiment of the invention. Thus, the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.